A primary goal of the Mackall laboratory is the development of immune based therapies for childhood cancer. A primary focus in this regard has been in developing consolidation immunotherapy for childhood cancer. Because standard upfront therapies for childhood cancer often induce complete remission or a very good partial remission (even in incurable disease), we hypothesize that delivering immune based therapy as a consolidative treatment will improve outcomes. This is based upon a large body of evidence demonstrating that immune responses are most effective when directed toward low burden disease and evidence that immune responses may be potentiated by lymphopenia, which exists in nearly all pediatric cancer patients following dose intensive standard therapy. To this end, we seek to integrate immune based therapies into the existing therapeutic armamentarium, by administering immunotherapy immediately following completion of standard multiagent chemotherapy. We hypothesize that immunotherapy will be more effective against minimal residual cancer than against bulky tumors due to a more favorable immune cell:tumor cell ratio and the absence of an organized immunosuppressive microenvironment. Previous work from the Mackall laboratory directly demonstrated that immune responses are more effective at eradicating minimal residual neoplastic disease that primary bulky tumor (Merchant, Cancer Immun and Immunoth, 2006). Furthermore, our expertise in the biology of T cell depletion provides us with unique insights regarding how best to deliver immune based therapy following cytotoxic chemotherapy, which the vast majority of childhood cancer patients receive as part of standard therapy. Because our translational research program has targeted childhood sarcomas, it is critical that we maintain an active clinical program in this arena, which provides the necessary referral network to conduct clinical trials in pediatric cancers and the necessary biologic specimens to conduct studies of relevance to human disease. Results of our first- and second-generation studies of consolidative immunotherapy were previously published (Medical and Pediatric Oncology 2002, Nature Medicine 2005 and Clin Canc Res 2008). During FY2011 we completed accrual of patients with pediatric sarcomas on a trial of immune based therapy initiated in 2008. The trial directly translates our basic research by administering dendritic cell based tumor vaccines to patients with high-risk pediatric sarcomas rendered lymphopenic by standard chemotherapy. Patients also receive autologous lymphocytes depleted of suppressive T cells, rhIL7, and a helper antigen, keyhold limpet hemocyanin (KLH), to augment immune responses. This regimen is highly novel representing the first use of rhIL7 in children and the only current example of rhIL7 being used in the context of a tumor vaccine trial. A total of 44 patients have been enrolled and 20 have initiated immunotherapy. Of the remaining 24, we expect that 10 will initiate immunotherapy within FY11, while 4 are ineligible due to insufficient collection of tumor lysate/lymphocytes and 10 are unable due to progressive disease during primary therapy. Results thus far demonstrate vigorous immune responses to KLH, and significant immune responses to tumor lysate, enhanced immune reconstitution compared to historical trials that did not utilize rhIL7, as well as promising rates of disease free and overall survival. We anticipate that treatment on this trial will be completed during FY12 and we will initiate publication of these results at that time. A second major achievement of this project was submission of our results of a pilot study of allogeneic stem cell transplantation for patients with high risk pediatric sarcomas for publication. This study (NCI 02-c-0259) used a non-myeloablative allogeneic peripheral blood stem cell transplant for patients with matched sibling donors. We demonstrated that the approach was well tolerated with no treatment related mortality and also made the novel observation that patients with very high risk pediatric solid tumors experience increased chemoresponsiveness and prolonged survival despite recurrence post-allogeneic stem cell transplant. These results provide novel evidence for heretofore unappreciated interactions between chemosensitivity and the immune milieu which is potentially exploitable in non-transplant settings. This report has been submitted and is in revision in the Biology of Blood and Marrow Transplantation. Other achievements during FY11 included initiation of an allogeneic stem cell transplantation trial which incorporates activated NK cell infusions administered during the period of lymphopoenia following stem cell transplant. This is highly novel using activated NK cells for the first time in pediatric patients and using a novel artificial antigen presenting cell for expansion of these cells. Results are not yet available but the trial is open and the first patient has been accrued. Other accomplishments include continued accrual to the only Phase I study of anti-CTLA4 in pediatrics, targeting patients with pediatric melanoma. We have seen evidence for a partial response in a patient with melanoma and some evidence for disease stabilization. Interestingly, preliminary results suggest that children may experience increased autoimmune toxicity compared to adults, a finding which if verified, provides new insights into immunomodulating therapies in pediatrics. During FY11, we also opened the first trial using a genetically engineered T cell receptor targeting children with sarcomas. Specificially, we will administer a T cell receptor targeting NY-ESO-1 in pediatric and adult patients with NY-ESO-1+HLA-A2+ synovial sarcoma. This trial seeks to reproduce promising results seen in a trial administering similar T cells with high dose IL2 to patients with sarcoma and melanoma and represents a collaboration with the University of Pennsylvania and Washington University in St. Louis. Because synovial sarcoma comprises a significant number of sarcomas seen in pediatrics, this trial is important to initiate in the pediatric population.